Predation on Ostracods

A bluegill (Lepomis macrochirus), a predator of ostracods.

Ostracods can be consumed by chance (e.g. by water birds foraging in sediments and water plants), or by animals actively seeking them. Typically, ostracods make up a small part of the diet of predators, but some predators, including the siphonophore Hippopodius hippopus and some species of water mites, feed exclusively on ostracods (Purcell 1981; Proctor & Pritchard 1989).

The consumption of ostracods can affect the capability of the midshipman fish of the Pacific coast of North America to bioluminesce. Those that live in the same area as bioluminescent ostracods and hence can eat them are able to produce light from the 700+ small dermal photophores on their heads and trunks. Those fish further north where bioluminescent ostracods do not live, do not bioluminesce. However, if northern midshipman fish are fed bioluminescent ostracods, they too can emit light (Thompson & Tsuji 1989).

Predator

Notes

References

Fish (Osteichthyes)

A wide variety of both marine and freshwater fish have been reported to prey on ostracods

Most amphipods are detritivores or scavengers, but predatory amphipods will eat ostracods.

Dauby et al. 2001

Bathynellaceans (Crustacea, Bathynellacea)

Some species of these blind, groundwater crustaceans prey on groundwater ostracods.

Cho et al. 2006

Copepods (Crustacea, Copepoda)

Ostracods form a small part of the diet of some species of freshwater copepods.

Fryer 1957

Other ostracods (Crustacea, Ostracoda)

Studies have shown that a small part of the diet of the marine giant ostracod Gigantocypris muelleri is made up of other ostracods, and marine planktonic halocyprid ostracods are consumed by Macrocypridina castanea. In non-marine habitats, Australocypris insularis was reported to feed on other smaller ostracod species, while Heterocypris incongruens is known to be cannibalistic.

A review listed 22 identified species of mites that prey on ostracods. Seven of these species prey only on ostracods.

Davids et al. 1981; Proctor & Pritchard 1989

Siphonophores (Cnidaria, Hydrozoa, Siphonophorae)

Many of these colonial hydrozoans are selective feeders, and one species (Hippopodius hippopus) feeds exclusively on ostracods.

Purcell 1981

Jellyfish (Cnidaria, Hydrozoa, Scyphozoa)

Ostracods are a prominent component of the diets of some species of jellyfish.

Sørnes et al. 2008

Anthozoans (Cnidaria, Anthozoa)

Ostracod remains have been recovered from both sea anemones and soft corals.

Sebens & Koehl 1984

Sea urchins (Echinodermata, Echinoidea)

A study showed that ostracods form part of the diet of a species of sea urchin, while another report noted that a sea urchin was gorged with ostracods.

Neale 1983; Penchaszadeh et al. 2004

Carnivorous plants

The bladderwort Utricularia preys on microcrustaceans, including ostracods.

Harms 2002

Note that in some cases it is not clear if the consumption of ostracods is a result of predation or scavenging of already dead ostracods. For example, Baird (1850) noted that freshwater ostracods can be seen eating the dead carcasses of other ostracod species, but it is unclear if this is predatory or scavenging behaviour.

Ostracods have also been recovered from the stomachs of neon flying squids, but these are considered to be transit food items, i.e. not consumed directly, but were introduced into the squid stomachs from the stomachs of the squids' prey, such as plankton-eating fish (Nigmatullin et al. 2009).

Anti-predation strategies

The jumping ostracod Tanycypris centa

1. Run (jump) away
Ostracods are generally very mobile, and will often try to escape danger either by swimming or crawling away.

One genus of freshwater ostracods, Tanycypris, has been observed preforming powerful jumps with its caudal rami, reaching speeds of 0.75 m/s. It is thought that such jumps are a predator response mechanism (Matzke-Karasz et al. 2014).

2. Hide
In experiments with juvenile flounder and ostracods from the Baltic Sea, it was noted that ostracods on an algal mat seem to be less predated on compared with those on a sand substrate (Aarnio & Mattila 2000). Other experiments have demonstrated that freshwater ostracods change their behaviour when fish are present, moving from open water to the relative safety of water plants (Roca et al. 1993; Uiblein et al. 1994; Kiss 2004). The colouration of some species of ostracods, especially ones with patches and stripes, acts as camouflage.

3. Live somewhere that predators can't tolerate.
Some species of ostracods, such as some giant ostracod species in Australia, live in saline lakes, with salinities too high to be tolerated by fish (Halse & McRae 2004). Other non-marine species are common in temporary water bodies, for example, seasonal lakes and rice fields. The dry periods of these habitats, tolerated by ostracods via their desiccation-resistant eggs, excludes some predators, such as fish. Small habitats, including springs and puddles, also exclude larger predators.

4. Light bomb the attacker
The myodocopid ostracod genus Vargula (sea firefly) is famous for its bioluminscence, used for mating and predator deterrence. If attacked by planktivorous fish, Vargula produce a bright and large (several cm) 'bomb-like' cloud of luminescence. Lasting for many seconds to more than a minute, this bright light probably startles and temporarily blinds the fish and sometimes causes the ostracod to be regurgitated.
The luminescence can also attract larger fish, which in turn may predate on the initial predator. When attacked, the initial predator may eject the contents of its stomach, thus the Vargula can survive the encounter. Such predatory attacks on Vargula are reported to be rare, as fish appear to avoid them (Morin 1986).

A female Vargula, length about 2.4 mm

Bioluminescent Vargula in a small petri dish

5. Close the carapace and wait

Side view of a tightly closed carapace. Note how one valve overlaps the other, creating a tight seal.

If all else fails there is one last hope. Tightly close the carapace and wait. Very small fish may have a go at eating a passing ostracod, but are often rapidly spat out; the hard carapace is too tough for very young or small fish to crush. With larger fish and better developed teeth, ostracods may not fair so well.

If the ostracod can survive the gauntlet of the teeth intact it is possible for it to survive passage through the gut. Juvenile flounder in the Baltic Sea feed on ostracods (amongst other things) during the first few years of life, but up to 75% of ostracods eaten survive passage through the gut (Aarnio & Bonsdorff 1997). Other experiments have shown that freshwater ostracods can also reduce predation from fish by resisting digestion, with up to 26% emerging from the gut alive (Vinyard 1979).

Ostracods passing through the guts of tadpoles, waterfowl, and even rodents (only in experiments) intact and alive have also been reported (Lopez et al. 2002). This ability to survive passage through guts of various animals probably helps with dispersal (Brochet et al. 2010).

Kiss, A. 2004. Field and laboratory observations on the microhabitat and food selection as well as predator avoidance of Notodromas monacha (Crustacea: Ostracoda). Revista Española de Micropaleontología, 36, 147-156.

Tszydel, M. & Grzybkowska, M. 2011. Diet and secondary production of some species of Hydropsyche larvae (Trichoptera: Hydropsychidae) in the tailwater affected by dam removal and the emptying of an impoundment. Zoosymposia, 5, 465-480.